Gelatin is a derivative of collagen, a principal structural and connective protein in animals. Gelatin is derived from denaturation of collagen and contains polypeptide sequences having Gly-X-Y repeats, where X and Y are most often proline and hydroxyproline residues. These sequences contribute to triple helical structure and affect the gelling ability of gelatin polypeptides. Currently available gelatin is extracted through processing of animal hides and bones, typically from bovine and porcine sources. The biophysical properties of gelatin make it a versatile material, widely used in a variety of applications and industries. Gelatin is used, for example, in numerous pharmaceutical and medical, photographic, industrial, cosmetic, and food and beverage products and processes of manufacture. Gelatin is thus a commercially valuable and versatile product.
Manufacture of Gelatin
Gelatin is typically manufactured from naturally occurring collagen in bovine and porcine sources, in particular, from hides and bones. In some instances, gelatin can be extracted from, for example, piscine, chicken, or equine sources. Raw materials of typical gelatin production, such as bovine hides and bones, originate from animals subject to government-certified inspection and passed fit for human consumption. There is concern over the infectivity of this raw material, due to the presence of contaminating agents such as transmissible spongiform encephalopathies (TSEs), particularly bovine spongiform encephalopathy (BSE), and scrapie, etc. (See, e.g., Rohwer, R. G. (1996), Dev Biol Stand 88:247–256.) Such issues are especially critical to gelatin used in pharmaceutical and medical applications.
Recently, concern about the safety of these materials, a significant portion of which are derived from bovine sources, has increased, causing various gelatin-containing products to become the focus of several regulatory measures to reduce the potential risk of transmission of bovine spongiform encephalopathy (BSE), linked to new variant Creutzfeldt-Jakob disease (nvCJD), a fatal neurological disease in humans. There is concern that purification steps currently used in the processing of extracting gelatin from animal tissues and bones may not be sufficient to remove the likelihood of infectivity due to contaminating SE-carrying tissue (i.e., brain tissue, etc.). U.S. and European manufacturers specify that raw material for gelatin to be included in animal or human food products or in pharmaceutical, medical, or cosmetic applications must not be obtained from a growing number of BSE countries. In addition, regulations specify that certain materials, e.g., bovine brain tissue, are not used in the production of gelatin.
Current production processes involve several purification and cleansing steps, and can require harsh and lengthy modes of extraction. The animal hides and bones are treated in a rendering process, and the extracted material is subjected to various chemical treatments, including prolonged exposure to highly acidic or alkaline solutions. Numerous purification steps can involve washing and filtration and various heat treatments. Acid demineralization and lime treatments are used to remove impurities such as non-collagenous proteins. Bones must be degreased. Additional washing and filtration steps, ion exchanges, and other chemical and sterilizing treatments are added to the process to further purify the material. Furthermore, contaminants and impurities can still remain after processing, and the resultant gelatin product must thus typically be clarified, purified, and often further concentrated before being ready for use.
Commercial gelatin is generally classified as type A or type B. These classifications reflect the pre-treatment extraction sources receive as part of the extraction process. Type A is generally derived from acid-processed materials, usually porcine hides, and type B is generally derived from alkaline- or lime-processed materials, usually bovine bones (ossein) and hides.
In extracting type A gelatin, the process generally involves subjecting fresh or frozen porcine hides to successive washings with water and treatments with dilute acids. The acid-treated skins are washed again and are then subject to repeated extraction steps in which they are treated with hot water, partially hydrolyzing the collagen present. The resultant extracts, dilute solutions of gelatin, are filtered and evaporated, and the resultant concentrates are allowed to cool or chilled to a gel. The gel is subsequently treated in drying tunnels, or by continuous dryers or other drying devices.
In the limed process, type B gelatin is derived from donor hides and skin trimmings washed and then treated with lime. The lime treatment can take as long as from one to three months, and is usually around sixty days. The limed hides are washed and treated with dilute acids. The hides are then hydrolyzed with hot water and the resulting extracts are processed as described above for the acid-treatment process.
Type B gelatin can also be processed from ossein sources. The hard bones are washed, degreased, and leached with successive treatments of dilute acids, such as hydrochloric acid. The acid treatment reacts with the mineral contents of bone, which are removed along with the acidic solution, leaving ossein, or demineralized bones. This organic bone matter, washed free of residual acid, is dried for storage or immediately limed. After liming, ossein is subsequently treated as described above for the production of gelatin from bovine hides. In all cases, after final filtering, demineralization, concentration, and drying steps, the resultant gelatin product is divided into batches, subjected to various physical, chemical, and bacteriological tests to determine grade and purity, and ground and blended according to commercial requirements. In both type A and B extraction processes, the resultant gelatin product typically comprises a mixture of gelatin molecules, in sizes of from a few thousand up to several hundred thousand Daltons.
Fish gelatin, classified as gelling or non-gelling types, and typically processed as Type A gelatin, is also used in certain commercial applications. Gelling types are usually derived from the skins of warm water fish, while non-gelling types are typically derived from cold water fish. Fish gelatins have widely varying amino acid compositions, and differ from animal gelatins in having typically lower proportions of proline and hydroxyproline residues. In contrast to animal gelatins, fish gelatins typically remain liquid at much lower temperatures, even at comparable average molecular weights. As with other animal gelatins, fish gelatin is extracted by treatment and subsequent hydrolyzation of fish skin. Again, as with animal extraction processes, the process of extracting fish gelatin results in a product that lacks homogeneity.